From e688bfbda0f6893b08d1e51f4fb26d4b38e922d4 Mon Sep 17 00:00:00 2001

From: Christian Borntraeger <borntraeger@de.ibm.com>

Date: Fri, 10 Aug 2012 15:11:45 +0200

Subject: [PATCH] qemu: Use valgrind annotations to mark kvm guest memory as

 defined

valgrind with kvm produces a big amount of false positives regarding

"Conditional jump or move depends on uninitialised value(s)". This

happens because the guest memory is allocated with qemu_vmalloc which

boils down posix_memalign etc. This function is (correctly) considered

by valgrind as returning undefined memory.

Since valgrind is based on jitting code, it will not be able to see

changes made by the guest to guest memory if this is done by KVM_RUN,

thus keeping most of the guest memory undefined.

Now lots of places in qemu will then use guest memory to change behaviour.

To avoid the flood of these messages, lets declare the whole guest

memory as defined. This will reduce the noise and allows us to see real

problems.

In the future we might want to make this conditional, since there

is actually something that we can use those false positives for:

These messages will point to code that depends on guest memory, so

we can use these backtraces to actually make an audit that is focussed

only at those code places. For normal development we dont want to

see those messages, though.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

Signed-off-by: Avi Kivity <avi@redhat.com>

(cherry picked from commit 62fe83318d2fc5b31f473d66326910d94c1c4907)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

---

 configure | 3 ++-

 kvm-all.c | 7 +++++++

 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/configure b/configure

index d7a948f..8874eff 100755

--- a/configure

+++ b/configure

@@ -2937,11 +2937,12 @@ if compile_prog "-Werror" "" ; then

 fi

 ########################################

-# check if we have valgrind/valgrind.h

+# check if we have valgrind/valgrind.h and valgrind/memcheck.h

 valgrind_h=no

 cat > $TMPC << EOF

 #include <valgrind/valgrind.h>

+#include <valgrind/memcheck.h>

 int main(void) {

   return 0;

 }

diff --git a/kvm-all.c b/kvm-all.c

index badf1d8..90c71f9 100644

--- a/kvm-all.c

+++ b/kvm-all.c

@@ -39,6 +39,10 @@

 #include <sys/eventfd.h>

 #endif

+#ifdef CONFIG_VALGRIND_H

+#include <valgrind/memcheck.h>

+#endif

+

 /* KVM uses PAGE_SIZE in its definition of COALESCED_MMIO_MAX */

 #define PAGE_SIZE TARGET_PAGE_SIZE

@@ -1769,6 +1773,9 @@ void *kvm_vmalloc(ram_addr_t size)

 void kvm_setup_guest_memory(void *start, size_t size)

 {

+#ifdef CONFIG_VALGRIND_H

+    VALGRIND_MAKE_MEM_DEFINED(start, size);

+#endif

     if (!kvm_has_sync_mmu()) {

         int ret = qemu_madvise(start, size, QEMU_MADV_DONTFORK);

-- 

1.7.12.1